Best Management Practices:
Controlled Drainage
Traditionally, the goals of drainage were to:
- Maximize crop yield and
- Minimize costs of drainage installation.
Reducing water quality effects of drainage is becoming a third objective in drainage design.
Nitrate loss is the biggest water quality concern related to tile drainage. Several new technologies can reduce nitrate loss. Controlled drainage keeps the water table high during the off-season when crops are not growing. The high water table increases the rate of denitrification (a process that converts nitrate to harmless nitrogen gas (N2) as soon as the saturated soil warms up in the spring) and reduces nitrate loss to the environment.
Controlled drainage can be combined with subirrigation to improve yields while protecting water quality. Subirrigation is irrigation back through the subsurface drain tiles. Subirrigation may be economical when fields are relatively level and need to be drained anyway, since additional infrastructure consists mainly of increased numbers of tiles the pumping system. One system being developed in Ohio combines a wetland for water treatment and a pond serving as a reservoir for subirrigation with a drainage system. This system has been shown to increase yields and reduce water quality impacts of drainage, although it is costly.
Info derived from: http://www.epa.gov/oecaagct/ag101/cropdrainage.html#bmps